6of7Pilots go through final check lists as crews prepare to fly T-6A aircraft at Joint Base San Antonio-Randolph on March 2, 2018.Photo: Tom Reel, Staff / San Antonio Express-News

7of7Photo of T-6A Texan II. The plane in the photo is flown by Lt. Col. David "Rev" Baker, who served as the T-6A's program manager in early 1999. Courtesy Photo, Master Sgt. David Richards, USAF. (U.S. Air Force photos by MSgt. Dave Richards)Photo: Master Sgt. David Richards, USAF / USAF

The head of the Air Force training command said Tuesday that pilots suffering mysterious physiological episodes in the T-6A Texan II sometimes received varying amounts of oxygen from an onboard system, in some cases less than half of what it was capable of delivering.

Lt. Gen. Steven Kwast said blame for the problem rested with the system, a device designed to pump fresh air to pilots as they fly at high altitudes. He said “the good news is it has nothing to do with the mix of gases” in the cockpit of the plane itself, describing the air in it as “safe and effective.”

Oxygen levels, however, can lurch from from as low as 40 percent to 100 percent, a fluctuation that some pilots have no trouble with during a flight — though not in all cases.

“It’s that fluctuation that we’re finding is the human body, on some days it does just fine with that because the normal mechanisms in your body adjust, but sometimes - and we’re not sure exactly why, if you’re tired, if you’re dehydrated or whatever it might be … that dynamic can create what feels like physiological instances or hypoxia, for example,” Kwast said.

Kwast’s comments, made during a media roundtable at the Air Force Association’s Air, Space & Cyber Conference in National Harbor, Maryland, came only hours before the crash of a T-6A in a field near Rolling Oaks Mall. Both pilots ejected.

The Air Force confirmed the crash, but had no information on the cause.

Failures in the plane’s oxygen system have so far resulted in at least 61 reported unexplained physiological episodes during the first six months of this year and triggered an Air Force, Navy and NASA investigation.

The San Antonio-based Air Education and Training Command last week said the investigation had found that varying levels of oxygen in the cockpit was the major factor in unexplained physiological episodes.

The problem has alarmed T-6 pilots and their families. As many as 11 pilots with the 12th Flying Training Wing had refused to fly the aircraft earlier this year. A squadron commander, Lt. Col. J.C. Gorman, halted flight operations June 25 after pilots expressed concerns about the safety of the Texan II, the primary Air Force trainer. The resumed flying the next day.

The Navy, too, has struggled to cope with a rising number of physiological episodes in its T-45C Goskawk trainer since 2014. In January 2017, a significant increase in severity and frequency of physiological events related to the oxygen system occurred and continued through March.

Reacting to the problem, 49 T-45 Goshawk instructor pilots at training bases in Florida and Texas bases refused to fly the plane at the end of March. The T-45 fleet resumed modified flight operations in mid-April for instructors, using a modified mask that circumvented the oxygen system.

Even as the Air Force has said it believes it has found the root cause of the oxygen problem, the Navy said Tuesday it had not. It said in a release Tuesday that “progress has been made in understanding and applying mitigation of both types of physiological episodes,” but “the trends have not been reversed or a root cause identified.”

The Air Force has been tight-lipped about its safety investigation. After pilots told the Express-News about a Randolph instructor pilot who suffered a physiological incident that left him struggling to recall parts of the mission the next day, commanders ordered that reports of such episodes be covered by safety privilege, which forbids public discussion about them.

Kwast said Tuesday that the severity of the Air Force’s episodes has been “very, very low,” and added that the issue would be made clear when the Safety Investigation Report is released. A training command spokeswoman later cautioned that the entire report would not be released, but parts of it would be provided to the media.

He did not say which bases had reported physiological episodes.

“So you’ll see some of those numbers come out, but that’s the bottom line takeaway is they are outliers, they are minor, but again, our responsibility is to really know what’s going on in the physics here and making sure we are doing everything in our power to make sure we have safe and effective aircraft for our air crew to train in,” Kwast said.

Sig Christenson covers the military for the San Antonio Express-News and been with the paper since 1997. He was embedded with the 3rd Infantry Division during the invasion of Iraq in 2003, and has reported from Baghdad and Afghanistan seven times since.

A Houston native, he covered the Branch Davidian siege, the 1994 Pensacola abortion clinic shooting, the 2003 space shuttle breakup over Texas, the 2009 Fort Hood shooting and its subsequent legal proceedings, as well as hurricanes, tropical storms and floods since 1986, among them Rita and Katrina and Maria.

Some of his projects include “Witness to War,” a special section recounting the invasion and early occupation of Iraq, and “The Only Retreat,” a three-part series detailing the only U.S. defeat during the invasion.

He’s won awards from Hearst Newspapers and the Associated Press, including Texas APME’s Specialties Reporting category in 2008, and was named “Reporter of the Year” by his peers in 2004.

A graduate of the University of Houston, he is a co-founder, former president and former board member of Military Reporters & Editors, established in 2002.

For a look at his work over time, see www.sigchristenson.com E-mail Sig at saddamscribe@yahoo.com